1. Field of the Invention
The present invention relates generally to automatic transmissions, and more particularly to a unique manual valve arrangement which provides for uninterrupted friction element control while manual valve porting is being switched. The unique manual valve arrangement provides for a failsafe mode of operation, and an energy savings logic mode of operation.
2. Background and Summary of the Invention
Conventional automatic transmissions include a hydrodynamic torque converter to transfer engine torque from the engine crankshaft to a rotatable input member of the transmission through fluid flow forces. The transmission includes frictional units which couple the rotating input member to one or more members of a planetary gear set. Other frictional units hold members of the planetary gear set stationary during flow of power. The drive clutch assemblies can couple the rotating input member of the transmission to the desired elements of the planetary gear sets, while the other frictional elements hold elements of these gear sets stationary. Such transmission systems also typically provide for one or more planetary gear sets in order to provide various ratios of torque and to ensure that the available torque and the respective reactive power demand are matched to each other.
Automatic transmissions are typically provided with a hydraulic control system and associated electronic controller which take automatic control of the friction units, gear ratio selecting, and gear shifting. The hydraulic control system includes various fluid passages connected between valves which are controllable for applying and releasing the friction clutch elements in order to shift the gears of the transmission based upon the controls provided by the electronic controller. The electronic controller typically chooses the proper gear dependant upon a shift program selection, accelerator position, engine condition, and vehicle speed. The hydraulic control system uses several valves to direct and regulate the supply of hydraulic pressure to the clutch elements. The hydraulic pressure control causes either the actuation or de-actuation of the respective frictional clutch units for effecting gear ratio changes in the transmission. The valves used in the hydraulic control circuit typically comprise spring-biased spool valves, spring-biased accumulators and ball check valves. Since many of the valves rely upon springs to provide a predetermined amount of force, it will be appreciated that each transmission design represents a finely tuned arrangement of interdependent valve components.
Conventional automatic transmissions rely upon electronic controls. Accordingly, if a malfunction in the controller or electronics occurs, the vehicle may be rendered inoperable. Thus, it is an object of the present invention to provide a failsafe operation where the vehicle can be operated by movement of the manual valve (manually movable with a PRNDL shift lever) in order to engage certain clutch elements of the automatic transmission. According to this aspect of the present invention, a hydraulic control system is provided for an automatic transmission including a planetary gear system having at least one clutch element engagable to change the torque ratio of the transmission. The hydraulic control system includes a pressurized fluid source, a manual valve selectively movable between a plurality of positions in communication with the pressurized fluid source. A first fluid passage communicates with the at least one clutch element and the manual valve. The first fluid passage includes a normally closed solenoid valve. A second fluid passage communicates with the at least one clutch element and the manual valve and includes a normally open solenoid valve. The hydraulic control system is capable of engaging the at least one clutch element with the manual valve in a predetermined position and the normally closed solenoid valve in an energized, open state and the normally open solenoid valve in an energized, closed state. The hydraulic control system is further capable of engaging the at least one clutch element with the manual valve in the predetermined position and the normally closed and the normally open solenoid valve de-energized. In this state of operation, the hydraulic control system is provided with a failsafe mode of operation which does not require the electronic controls.
Hydraulic control systems often include a manual valve which can be operated to selectively engage various clutches of the planetary gear system. However, during movement of the manual valve, interrupted friction element control typically occurs. The present invention provides a unique manual valve arrangement which provides for uninterrupted friction element control while manual valve porting is being switched. Thus, the engagement of certain clutch elements can be maintained even though manual valve porting is switched between a drive position and a second or low position.
The unique manual valve and solenoid arrangement of the present invention also permits an energy savings logic to be used. Since in some gear positions a multi-select solenoid is connected to the friction element which is being applied, application of the friction element can be maintained by turning electrical power off to both of the solenoids thereby saving electrical power.
With conventional automatic transmission designs, the lubrication and cooler systems are provided in series. Thus, when the lubrication system is under high demand, lubrication starvation can become a problem. The transmission of the present invention has a unique arrangement of lube and cooler circuits. The lubrication and cooler circuits are fed in parallel. One path which provides gear train lubrication flow is maintained with a regulated pressure so that regardless of the demand which may increase due to centrifugal effects, the control pressure is maintained in order to regulate lubrication flow in order to meet component lubrication requirements. The cooler circuit is routed through the torque converter then to the cooler which is directed back into the pump suction. By routing the fluid into the pump inlet, a portion of the fluid energy is saved by using fluid velocity to help fill the pump.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.